In the following code example, we have an class for immutable objects that represents a room. North, South, East, and West represent exits into other rooms.
public sealed class Room
{
public Room(string name, Room northExit, Room southExit, Room eastExit, Room westExit)
{
this.Name = name;
this.North = northExit;
this.South = southExit;
this.East = eastExit;
this.West = westExit;
}
public string Name { get; }
public Room North { get; }
public Room South { get; }
public Room East { get; }
public Room West { get; }
}
So we see, this class is designed with a reflexive circular reference. But because the class immutable, I'm stuck with a 'chicken or the egg' problem. I'm certain that experienced functional programmers know how deal with this. How can it be handled in C#?
I'm endeavoring to code a text-based adventure game, but using functional programming principles just for the sake of learning. I'm stuck on this concept and can use some help!!! Thanks.
UPDATE:
Here's a working implementation based on Mike Nakis' answer regarding lazy initialization:
using System;
public sealed class Room
{
private readonly Func<Room> north;
private readonly Func<Room> south;
private readonly Func<Room> east;
private readonly Func<Room> west;
public Room(
string name,
Func<Room> northExit = null,
Func<Room> southExit = null,
Func<Room> eastExit = null,
Func<Room> westExit = null)
{
this.Name = name;
var dummyDelegate = new Func<Room>(() => { return null; });
this.north = northExit ?? dummyDelegate;
this.south = southExit ?? dummyDelegate;
this.east = eastExit ?? dummyDelegate;
this.west = westExit ?? dummyDelegate;
}
public string Name { get; }
public override string ToString()
{
return this.Name;
}
public Room North
{
get { return this.north(); }
}
public Room South
{
get { return this.south(); }
}
public Room East
{
get { return this.east(); }
}
public Room West
{
get { return this.west(); }
}
public static void Main(string[] args)
{
Room kitchen = null;
Room library = null;
kitchen = new Room(
name: "Kitchen",
northExit: () => library
);
library = new Room(
name: "Library",
southExit: () => kitchen
);
Console.WriteLine(
$"The {kitchen} has a northen exit that " +
$"leads to the {kitchen.North}.");
Console.WriteLine(
$"The {library} has a southern exit that " +
$"leads to the {library.South}.");
Console.ReadKey();
}
}
